WAN Considerations
For absorption over the WAN to be successful, you charge anxiously plan, design, and implement
various characteristics of the WAN itself. The Intra-Cluster Communication
Signaling (ICCS) amid UCM servers consists of abounding cartage types. The ICCS traffic
types are classified as either antecedence or best effort. Antecedence ICCS cartage is apparent with
IP Precedence 3 (DSCP 24 or PHB CS3). Best-effort ICCS cartage is apparent with IP
Precedence 0 (DSCP 0 or PHB BE).
The afterward architecture guidelines administer to the adumbrated WAN characteristics:
■ Delay: The best one-way adjournment amid any UCM servers for all antecedence ICCS
traffic should not beat 20 ms, or 40 ms round-trip time (RTT). Adjournment for other
ICCS cartage should be kept reasonable to accommodate appropriate database access.
Propagation adjournment amid two sites introduces 6 microseconds per kilometer without
any added arrangement delays actuality considered. This equates to a abstract maximum
distance of about 3000 km for 20 ms adjournment or about 1860
miles. These distances are provided alone as about guidelines and in absoluteness will be
shorter because of added adjournment incurred aural the network.
■ Jitter: Jitter is the capricious adjournment that packets acquire through the arrangement because of
processing, queue, buffer, congestion, or aisle aberration delay. Jitter for the IP
Precedence 3 ICCS cartage charge be minimized application QoS features.
■ Packet accident and errors: The arrangement should be engineered to accommodate acceptable prioritized
bandwidth for all ICCS traffic, abnormally the antecedence ICCS traffic. Standard
QoS mechanisms charge be implemented to abstain bottleneck and packet loss. If packets
are absent due to band errors or added “real world” conditions, an ICCS packet will be
retransmitted because it uses the TCP agreement for reliable transmission. The retransmission
might aftereffect in a alarm actuality delayed during setup, abstract (teardown), or
other added casework during the call. Some packet-loss altitude could
result in a absent call, but this book should be no added acceptable than errors occurring
on a T1 or E1, which affect calls via a block to the PSTN/ISDN.
■ Bandwidth: Provision the actual bulk of bandwidth amid anniversary server for the
expected alarm volume, blazon of devices, and cardinal of devices. This bandwidth is in
addition to any added bandwidth for added applications administration the network, including
voice and video cartage amid the sites. The bandwidth provisioned charge have
QoS enabled to accommodate the prioritization and scheduling for the altered classes of
traffic. The accepted aphorism for bandwidth is to overprovision and undersubscribe.
■ QoS: The arrangement basement relies on QoS engineering to accommodate constant and
predictable end-to-end levels of account for traffic. Neither QoS nor bandwidth alone
is a solution. Rather, QoS-enabled bandwidth charge be engineered into the network
infrastructure.