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VoIP FAQ for IP office

Computers in an office communicate via the LAN (Local Area Network). This at its simplest may be a length of coax cable connecting all the computers, or by twisted pair cables going into a central hub unit. The IP406 V2 supports an 8 port Layer 2 Ethernet switch. The Small Office Edition supports a 4 port Layer 2 ethernet switch with a fifth Ethernet port as a Layer 3 switch. The IP412 support a 2 port Layer 3 Ethernet Switching.
When computers communicate they do not care where the destination is. Their task is simply to pass the packet to the next machine and then forget about it. Where the destination is on another network, the router is the “gateway” to the rest of the world and its job is to cope with that traffic. The router alleviates the need to establish and hold the call for the duration of a remote communication session by automatically establishing a connection only when data is to be passed. Routers may be connected together using WAN (Wide Area Network) links that could be point-to-point leased lines, managed IP networks, Frame Relay networks or exchange lines (Central Office). IP Office platforms support all of these types of network connections.

The IP Office has a Wide Area Network (WAN) port that can be connected to a digital leased line service using either X.21 or V.35 interface at speeds up to 2048kbps. Point-to-Point protocol (PPP) is used over this link. The data within the call uses the Point-to-Point Protocol (PPP) which is used by the vast majority of manufacturers for linking routers. PPP support is essential if it is not the same manufacturer’s equipment at each end of the link.
Exchange lines (Central Office) can also be used in the event of failure of the WAN link or to provide alternate or top up bandwidth on demand.
All IP Office platforms have an integral router with support for bandwidth on demand that allows the negotiation of extra bandwidth dynamically over time. IP Office initiates extra calls between sites only when there is data to be sent or sufficient data to warrant additional channels. It then drops the extra channels when they are no longer needed. The calls are made automatically, without the users being aware of when calls begin or end. The rules for making calls, how long to keep calls up etc, are configurable within IP Office.
It is possible to have several different routing destinations or paths active at any time linking the office to other offices and the Internet simultaneously.

• IP Office - Small Office Edition & IP406 V2 Only.
All the IP Office - Small Office Edition platforms provide a four port Layer 2 Ethernet Switch. The IP406 V2 provides an 8 port Layer 2 Ethernet switch.
Each port auto-senses its operational speed, 10M or 100M. In addition to the four port layer 2 switch, IP Office - Small Office Edition has a fifth Ethernet port (labeled WAN) with its own IP Address (LAN2) intended for connecting to external xDSL or Cable Modems. This fifth port is a Layer 3 switch to the other four ports.

Integral 10/100 Mbit Layer 3 Ethernet Switch
• IP Office - Small Office Edition & IP412 Only.
The IP412 supports a two-port Layer 3 Ethernet switch. Both of these switched ports have their own IP addresses (LAN1 and LAN2). In order for traffic to pass from one port to the other a route is configured in the system’s routing tables.
Additionally, it is possible to set up a firewall between the two LAN segments. The IP Office - Small Office Edition offers similar functionality between its four port Layer 2 Ethernet switch and its Layer 3 Ethernet WAN port.
Layer 3 switching is particularly useful in situations where it is desirable to have a ‘trusted’ and ‘unsecured’ network, where the ‘unsecured’ network is uncontrolled and carries public traffic on it.

DHCP Server
DHCP: Dynamic Host Configuration Protocol, a standards-based protocol for dynamically allocating and managing IP addresses. DHCP runs between individual computers and a DHCP server to allocate and assign IP addresses to the computers and also limits the time computers can use the address. When time expires on the use of the IP address, the computers contact the DHCP server again to obtain an address.
IP Office can manage your IP Network for you through its integral DHCP Server. IP Office can be configured to hold a pool of IP addresses for users on the Local Area Network. When a user powers up their PC, the system will allocate them an IP address for the duration of their session. The DHCP server also provides the user’s PC with the address of the Domain Name Service (DNS) server and the Windows Name Service (WINS) server. Alternatively, for customers who have a separate DHCP Server, IP Office can be configured to obtain its address from that server or be set with its own dedicated static address. The IP Office - Small Office Edition & the IP412 have two independently controlled DHCP servers, one dedicated to each of the Layer 3 switched LANs.

What is Quality of Service?
Quality of Service (QoS) is a measure of the performance of a network that reflects the availability of network service and the quality of network transmissions. The term itself refers to a number of networking technologies and techniques and does not necessarily restrict itself to any single protocol or standard.
There are a number of measures that can be taken on the LAN and WAN to make them ‘good enough’ to carry voice traffic. Some of these are the implementation of standards based QoS protocols while are simply a matter of network architecture and good network management practices.
The term ‘good enough’ is intentional. Every customer will have different expectations and different budgets to work to. Some will be willing to upgrade their networks to use the best possible equipment and practices. To others the additional expense may be viewed as unnecessary.
Examples of standards based Quality of Service protocols include DiffServ and 802.1p/q.
DiffServ: DiffServ (RFC 2474) is a TCP/IP quality of Service mechanism used to ensure that IP packets are prioritized according to their importance, for example prioritization of voice packets over data packets. Prioritization is based upon the Type of Service (ToS) field in the IP header.

IP: The Internet Protocol (IP) is the method or protocol by which data is sent from one computer to another on the Internet. Each computer (known as a host) on the Internet has at least one IP address that uniquely identifies it from all other computers on the Internet. When you send or receive data (for example, an email note or a Webpage), the message gets divided into little chunks called packets. Each of these packets contains both the sender’s Internet address and the receiver’s address. Any packet is sent first to a gateway computer that understands a small part of the Internet. The gateway computer (or router) reads the destination address and forwards the packet to an adjacent gateway that in turn reads the destination address and so forth across the Internet until one gateway recognizes the packet as belonging to a computer within its immediate neighborhood or domain. That gateway then forwards the packet directly to the computer whose address is specified. Because a message is divided into a number of packets, each packet can, if necessary, be sent by a different route across the Internet. Packets can arrive in a different order than the order they were sent in. The Internet Protocol just delivers them. It’s up to another protocol, typically TCP, to put them back in the right order. IP is a connectionless protocol, which means that there is no established connection between the end points that are communicating.
Each packet that travels through the Internet is treated as an independent unit of data without any relation to any other unit of data. (The reason the packets do get put in the right order is because of TCP, the connection oriented protocol that keeps track of the packet sequence in a message.) In the Open Systems Interconnection (OSI) communication model, IP is in layer 3, the Networking Layer.

What are the Symptoms of Poor Speech?
Poor speech quality manifests itself in three distinct ways.
• Echo.
• Delays.
• Warble, that is ‘in a cave’ or underwater like sound.
• Clipping.
• Distortion.
• Disappearing speech, some words or parts of words missing.
• No speech or speech in one direction only.

What Causes Poor Speech Quality?
Poor speech quality can be caused by a number of different problems that can occur in most networking environments
• VoIP conversion delays.
• Network delays.
• Dropped traffic.
• Traffic being received at varying speeds.
• Inappropriate conversions from speech to VoIP.
• Multiple VoIP conversions.
in VoIP networks, unreliability in the network which can introduce large latencies or inconsistencies in the transmitted VoIP traffic and the actual process of converting speech to VoIP traffic and vice versa.

How Do I Minimize Delay Induced Echo?
Delay in a network originates from a number of different sources and phenomena.
A primary source of delay is the process of converting speech to VoIP traffic. The IP Office supports a number of standards based encoding methods to allow the optimum trade off between quality and bandwidth to be made
IP Office incorporates integral echo cancellation to minimize the effect of echo introduced in the VoIP conversion process.
Another source of delay comes from data and voice traffic queuing at the ports of switches, routers, gateways and or bridges that make up the network. It is possible that the traffic queuing at a port is minimal and no action needs to be taken. This would be the case if the available bandwidth far exceeded the demand. To overcome queuing bottlenecks in the network, IP Office prioritizes voice traffic using a standard known as DiffServ. This marks each IP packet carrying voice with a flag so that routers, etc. can force packets containing voice to the front of the transmission queue. An alternative method of prioritization that can be used by switches and routers, with an equally satisfactory result, is to look at what protocol is being used and prioritize this. All voice traffic is carried using two easily identifiable protocols, RTP and RTCP. Both methods are equally good, choose whichever method is the most cost effective and easiest to implement and manage.

A similar source of delay can be attributed to specific network nodes that convert from one network medium to another. For example T1 trunk lines may be carried across a high speed DSL like connection and converting from the high speed link back to T1 in the access gateway takes time to perform. Any VoIP traffic being carried through this link is therefore subject to the delay introduced by this conversion step. The delay may be minimized by ensuring that an appropriate QoS mechanism is enabled in the gateway to prioritize the VoIP traffic. IP Office incorporates integral echo cancellation to help minimize the effect of this kind of delay introduced by the network.
Delay can also be introduced as a consequent of collisions occurring on particular segments of the LAN. Collisions result when two devices on a shared switch port or segment try to transmit simultaneously. This causes all devices to stop transmitting for a period of time. This is a normal characteristic of many older Ethernet networks and, if occasional, may pass unnoticed. The more devices sharing a switch port, and the busier they are, the greater the opportunity for collisions. This is simply resolved by reducing the number of devices on each port, or by dedicating a port to each VoIP device. If you are just using VoIP to link two IP Offices together, it’s well worth dedicating a port to each IP Office and router at either end of the link as the cost implications are likely to be minimal. In this regard it is important to dimension a network to cope with existing traffic demands as well as any future increases in traffic carrying capability.

How Do I Minimize Warble and Clipping?
Warble, clipping and some distortion quality problems are symptoms of variable delay and or packet loss.
Variability in the delays of traffic is called jitter. Jitter and packet loss may be the result of switches and routers that are either faulty or working outside their design intentions.
IP Office provides jitter buffers to compensate for a moderate amount of jitter found in networks. Voice traffic is quite tolerant of small amounts of packet loss so in most cases this may be ignored. Where packet loss is excessive (greater than 2% say) the cause should be established and fixed. This could be due to a fault or simply an over worked device discarding packets. Significant packet loss can cause perceptible losses in speech, to the extent that no speech may be heard either in one or both directions.

How Do I Minimize Distortion?
Each time speech is converted into a digital signal and back again, tiny difference from the original creeps in. The more times this happens on a single call, the bigger those differences can become. These differences can become perceptible as distortion. Ideally, the path speech takes should only require one ‘analog to digital to analog’ conversion and this will be the case in many instances. Exceptions to this occur when making calls to mobile telephones or voice mail systems where the analog to digital to analog conversion may occur twice (once on IP Office and once on the mobile network, etc).
Different encoding methods will have different effects. IP Office supports a range of encoding methods to allow you to choose the one with the right quality versus bandwidth for your network. In general multiple conversions should be minimized wherever possible.

What Delay is Acceptable?
Try to keep the overall end-to-end delay to 150 milliseconds or below.
An idea of the delay inherent in the network can be measured by carrying out a ping test and dividing the result by two. IP Office has built in echo cancellation to maximize speech quality.

What is the Perfect Network?
For those customers who are willing to upgrade their infrstructure, the best preactice network would have every device on the LAN connected through its own dedicated port on a DiffServ capable layer 3 switch. Connections to the WAN should be through devices that support DiffServ, for instance IP Office.

Leased Line Support
All platforms are capable of connecting to leased line services. Six physical types of Leased Line are supported
X.21, V.35 and V.24, via the WAN port, or E1/T1 and Basic Rate via the trunk interfaces on the base unit. The
X.21, V35 and V24 are externally clocked and can operate at any speed up to and including 2M. E1/T1 trunks can be configured to operate in a fractional mode for ‘point to multi-point’ applications i.e. a single 2M interface could be treated as 3 x 512K and 8 x 64K going to 11 different locations. When using T1 as a Leased Line it is possible to use the same circuit for switched circuit services.

Point-to-Point Protocol (PPP)
PPP is an industry standard Wide Area Networking Protocol, that allows inter-working with a wide range of 3rd party routers. PPP is used over dial-up or leased line circuits where a single channel is used to connect the two locations together. e.g. A single channel maybe a 64K channel on a dial-up circuit or a 256K leased line etc.

Multi-Link Point-to-Point Protocol (ML-PPP)
IP Office supports Multi-Link PPP allowing additional calls to be made where bandwidth greater than a single channel is required. The maximum number of channels available to data can be set on a service-by-service basis. When the available bandwidth reaches a user defined limit additional channels can be automatically added. Similarly, when traffic falls then the number of channels in use can be automatically reduced. If there is no data traffic on any of the channels in use then all lines can be cleared. Since most carriers have a minimum charge for calls, the period that a channel has to be idle before clearing is configurable. Through these mechanisms call costs can be effectively controlled while ensuring that bandwidth is available as and when it is needed.

Frame Relay
Frame relay is a wide area networking protocol loosely based on ideas borrowed from the X.25 protocol. Individual network connections are multiplexed over a common medium by the use of Permanent Virtual Circuits (PVC). This allows a single Leased Line to provide connectivity to a number of different locations. Frame relay is currently implemented in IP Office as a CPE or ‘router end’ protocol over WAN connections. IP Office supports both PPP and RFC1490 encapsulation with fragmentation of large data packets to provide voice quality of service.

Network Address Translation (NAT)
NAT is a mechanism that allows you to use a different IP address to that of your internal network while connected to an external party or service. When connecting to the Internet, ISPs typically want a customer to use an IP address they have allocated. Using NAT this is easily accommodated, eradicating the need for the customer to change their network numbering scheme. Typically, a company maps its internal network addresses to a global external IP address and unmaps the global IP address on incoming packets back into internal IP addresses. This helps ensure security since each outgoing or incoming request must go through a translation process. This also offers the opportunity to qualify or authenticate the request or match it to a previous request. NAT also conserves the number of global IP addresses that a company needs.

Firewall
The integrated firewall provides an easy point and click configuration allowing the filtering of the most common IP protocols including File Transfer Protocol (FTP) and Internet browsing (HTTP). Each protocol passing through the firewall can be restricted/allowed access to.

VPN: IPSec Tunneling
IPSec tunnels allow a company to pass data between locations over unsecured IP networks such as the public internet. The corporate data is secured using 3DES encryption making it unintelligible to other parties that might be ‘eaves dropping’ on the traffic. Tunneling can be applied to link offices together or provide workers access to the office over the internet. All Platforms support up to a total of 256K worth of encrypted traffic to multiple locations. Initially, inter-working is supported only between IP Offices that are connected either directly on a WAN port or via the LAN using a 3rd Party router. IPSec is enabled on IP Office through a License Key.

VPN: Layer 2 Tunneling Protocol
PPP authentication using PAP or CHAP takes place between directly connected routers only. When using a public IP
Network to connect sites this authentication takes place between the customers router and the service provide router that it is connected to. In some circumstances it is desirable to authenticate between the customer owned routers, jumping over all the intermediary routers of the service provide network. Layer 2 Tunneling Protocol allow this to happen by facilitating a two stage authentication, firstly with the service provider router then the customer router on the remote network.