Server 2008 R2 introduces new technologies and refines existing ones to
maximize performance, replication, and file sharing and to reduce WAN
bandwidth utilization consumed between branch offices and hub sites. The
following technologies that address and improve bandwidth utilization,
latency, and reliability of the WAN links at a branch office include the
Read-Only Domain Controllers
The amount of information replicated over the WAN between a
Read-Only Domain Controller residing at a branch office and a writable
domain controller at a hub site is significantly minimized. This is
because changes do not originate at an RODC, eliminating the need to
replicate data from an RODC to a writable domain controller replication
partner at a hub site, resulting in a reduction of bandwidth and WAN
utilization being used.
Next Generation TCP/IP Stack
A tremendous amount of
improvement is seen in the Next Generation TCP/IP stack introduced in
Windows Server 2008 R2. Some of the features for the new TCP/IP stack
that directly impact and improve branch office WAN utilization and
replication include the following:
Receive Window Auto-Tuning—
Support for Receive Window Auto-Tuning is new in the Next Generation
TCP/IP stack. Receiver-side throughput is improved through Receive
Window Auto-Tuning because this feature is able to calculate the best
possible receive window size for each connection by taking into account
bandwidth, latency connection, and application retrieval rate. Bandwidth
performance naturally improves with better throughput. Bandwidth
performance can improve even more if all applications receive TCP data.
Compound TCP/IP (CTCP)—
Compound TCP/IP, which is most often used for TCP connections that have
a large receive window size in addition to a large bandwidth delay
product, ultimately improves receiver-side throughput. With CTCP, the
amount of data sent across connections is significantly greater;
however, TCP connections
are not impacted negatively. If CTCP and Receive Window Auto-Tuning are
used together, even more benefits, including increased link utilization
and performance gains for large bandwidth delay connections, can be
When a TCP segment is lost, TCP assumes that it was because of
congestion at a router, so it performs congestion control. This lowers
the TCP sender’s transmission rate. With Explicit Congestion
Notification (ECN) in the routing infrastructure, routers experiencing
congestion mark the packets as they forward them. TCP peers receiving
marked packets lower their transmission rate to ease congestion and
prevent segment losses. This increases the overall throughput between
Path maximum transmission unit (PMTU) black-hole router detection
automatically adjusts the PMTU for a connection when large TCP segments
RFC optimizations— The TCP/IP stack has better support for RFCs related to TCP communications.
The Next Generation TCP/IP stack supports neighbor unreachability
detection for IPv4 traffic. A computer such as a branch office maintains
status about whether neighboring computers such as a hub site are
reachable. This provides better error detection and recovery when
computers are not available.
Dead Gateway support—
Unlike the previous Windows versions of Dead Gateway Detection, the
Next Generation TCP/IP Dead Gateway support now provides a failover and
failback mechanism when encountering dead gateways.
Distributed File System (DFS)
DFS in Windows Server 2008
R2 builds upon the completely revised replication engine in Windows
Server 2003 R2. DFS, which was first introduced with Windows 2000
Server, provides a robust multimaster file replication service that is
significantly more scalable and efficient in synchronizing file servers
than its predecessor, File Replication Service (FRS).
With Windows Server 2008
R2, DFS includes an impressive list of benefits for both Active
Directory and branch office server management, including simplified
branch server management, reduction of backups, and more efficient
storage management. In addition, DFS Replication (DFSR) enhances branch
office implementations because it is possible to schedule and throttle
replication schemes, support multiple replication topologies, and
utilize Remote Differential Compression (RDC) to increase WAN
efficiency. If WAN connections fail, data can be stored and forwarded
until WAN connections become available. As a result, WAN replication is
reduced and optimized, branch office mission-critical files can be
replicated among branch offices, hub sites can reduce the amount of IT
management that takes place in the branch office, and the need for
backups can also be reduced.
Additionally, a new feature
that was introduced in Windows Server 2008 R2 is support for read-only
copies of information stored in Distributed File System (DFS) replicas.
that is stored on a read-only DFS replica is read-only, users are not
able to modify/delete/create the replicated content. Therefore,
information that is stored in a read-only DFS replica is protected at
branch office locations from accidental modification.
Windows Server 2008 R2 now uses
DFSR to replicate Group Policy Objects between domain controllers
within a domain. By leveraging DFSR differential replication, changes
only occur between two domain controllers and not all of the domain
controllers as in the past. As a result, the amount of bandwidth
required during Group Policy replication is greatly reduced.
Group policies, which are the
traditional Administrative Template files, are now replaced with new
XML-based files called ADMX in Windows Server 2008 R2. Moreover, the new
ADMX files are stored in a centralized store within SYSVOL. Thus, the
new templates, storage of group policies, and utilization of DFSR for
replication improve branch office solutions because less data needs to
be replicated between the branch office and hub site.
SMB Version 2.0
Another enhancement for
Windows Server 2008 R2 branch office deployments is the server message
block (SMB) protocol version 2.0. SMB, originally invented at IBM, is an
application-level network file-sharing protocol mainly applied when
accessing files, printers, serial ports, and miscellaneous
communications between computers on a network.
The protocol hasn’t evolved
much since it was originally created 15 years ago. As a result, the
protocol is considered to be overly chatty and generates unnecessary
network traffic between computers on a network. This especially hinders
users at branch office implementations when accessing files over the WAN
to a hub site, especially if the WAN link is slow or already congested.
the concerns and limitations with the existing version of SMB and has
completely rewritten SMB to meet the demand of today’s branch office
needs. The benefits and improvements of the new SMB version 2.0 protocol
on WAN network performance and end-user experience when transferring
data between the branch office and hub sites include the following:
Efficiency, performance, and data streaming are improved and are four to five times faster than the older version of SMB.
The client can increase parallel requests.
Offline capabilities are included, which is beneficial on slow networks and improves the end-user experience.
Synchronization performance for offline files is improved.
Multiple client requests can be compounded into a single round-trip.
Users can now work in offline mode and synchronize changes on demand.
Server scalability has been increased by reduced per-connection resource usage.
The amount of bandwidth required for network communications has been dramatically reduced.