Network design
304 Avaya Application Solutions IP Telephony Deployment Guide
In many organizations, because of the expense of dedicated WAN circuits, dial-on-demand
circuits are provisioned as backup if the primary link fails. The two principal technologies are
ISDN (BRI) and analog modem. ISDN dial-up takes approximately 2 seconds to connect, and
offers 64 Kbps to 128 Kbps of bandwidth. Analog modems take 60 seconds to connect, and
offer up to 56 Kbps of bandwidth. If G.729 is used as the codec, either technology can support
IP Telephony traffic. If G.711 is used as the codec, only ISDN is appropriate. Also, because of
the difference in connect times, ISDN is the preferred dial-on-demand technology for
implementing IP Telephony.
Multipath routing
Many routing protocols, such as OSPF, install multiple routes for a particular destination into a
routing table. Many routers attempt to load-balance across the two paths. There are two
methods for load balancing across multiple paths. The first method is per-packet load
balancing, where each packet is serviced round-robin fashion across the two links. The second
method is per-flow load balancing, where all packets in an identified “flow” (source and
destination addresses and ports) take the same path. IP Telephony does not operate well over
per-packet load-balanced paths. This type of setup often leads to “choppy” quality voice. Avaya
recommends that in situations with multiple active paths, per-flow load balancing is preferable to
per-packet load balancing. This behavior is enabled by default on Avaya products. On Cisco
routers, the command for this is “ip route-cache,” applied per interface.
Frame Relay
The nature of Frame Relay poses somewhat of a challenge for IP Telephony. This section
presents:
●
Overview of frame relay
●
A frame relay issue and alternatives
●
Additional frame relay information
Overview of frame relay
Frame Relay service is composed of three elements: the physical access circuit, the Frame,
Relay port, and the virtual circuit. The physical access circuit is usually a T1 or fractional T1 and
is provided by the local exchange carrier (LEC) between the customer premise and the nearest
central office (CO). The Frame Relay port is the physical access into the Frame Relay network,
a port on the Frame Relay switch itself.
The access circuit rate and the Frame Relay port rate must match. The virtual circuit is a logical
connection between Frame Relay ports that can be provided by the LEC for intra-lata Frame
Relay, or by the inter-exchange carrier (IXC) for inter-lata Frame Relay. The most common
virtual circuit is a permanent virtual circuit (PVC), which is associated with a committed
information rate (CIR). The PVC is identified at each end by a separate data-link connection
identifier (DLCI) in
Figure 79
.
Summary of Contents for Application Solutions
Page 1: ...Avaya Application Solutions IP Telephony Deployment Guide 555 245 600 Issue 3 4 1 June 2005 ...
Page 20: ...About This Book 20 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 21: ...Issue 3 4 1 June 2005 21 Section 1 Avaya Application Solutions product guide ...
Page 22: ...22 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 106: ...Call processing 106 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 124: ...Avaya LAN switching products 124 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 139: ...Issue 3 4 1 June 2005 139 Section 2 Deploying IP Telephony ...
Page 140: ...140 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 186: ...Traffic engineering 186 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 204: ...Security 204 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 228: ...Avaya Integrated Management 228 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 274: ...Reliability and Recovery 274 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 275: ...Issue 3 4 1 June 2005 275 Section 3 Getting the IP network ready for telephony ...
Page 276: ...276 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 356: ...Network recovery 356 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 366: ...Network assessment offer 366 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 367: ...Issue 3 4 1 June 2005 367 Appendixes ...
Page 368: ...Appendixes 368 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 394: ...Access list 394 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 414: ...DHCP TFTP 414 Avaya Application Solutions IP Telephony Deployment Guide ...